JP2001007024A - Method of forming of polycrystalline silicon film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a polycrystalline silicon substrate on a glass substrate at lower temperatures. SOLUTION: A microcrystal film 2 containing crystalline nuclei having a grain size of about 1,000 Å is formed on a glass substrate 1, and an amorphous silicon film 3 is formed on the film 2. Then a polycrystalline silicon film 4 is formed by annealing the films 2 and 3 with an excimer laser beam. Since crystals in the polycrystalline silicon film 4 grow from the microcrystals contained in the film as the nuclei, the grain sizes of the crystals can be mode larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a polycrystalline silicon film on a glass substrate, and more particularly to a method for forming a polycrystalline silicon film having a large grain size and high electron mobility.

[0002]

2. Description of the Related Art Liquid crystal display devices (Liquid Crystal Displa)
(y: LCD) is a display device in which liquid crystal is sealed between two opposing glass substrates. With the increase in the definition of LCDs, there is a demand for so-called system-on-glass in which various electrodes for driving liquid crystals and circuits for controlling the electrodes are formed on a glass substrate. For this purpose, a technique for forming a high-quality silicon thin film on a glass substrate at a low temperature is indispensable.

[0003] Even if the glass is a so-called heat-resistant glass obtained by adding alumina to silicon oxide, 640 ° C to 670 ° C.
Softens to a degree. Therefore, each step of forming electrodes and circuits on the glass substrate must be performed at least at a temperature lower than the softening point.

FIG. 5 is a sectional view showing a step of forming a conventional polycrystalline silicon film. Step 1: As shown in FIG. 5 (a), plasma CVD (Chemical Vapor Deposi) using a gas obtained by diluting higher-order silane such as silane (SiH ₄ ) or disilane (Si ₂ H ₆ ) with hydrogen.
), an amorphous silicon film 102 is formed on the glass substrate 101 to a thickness of about 500.
Then, the amorphous silicon film 102 is heated by, for example, an electric furnace to desorb hydrogen contained in the amorphous silicon film 102 to reduce the concentration in the film. Step 2: As shown in FIG. 5B, annealing is performed by irradiating the amorphous silicon film 102 with an excimer laser 103 such as ArF, KrF, or XeCl. The amorphous silicon in the region irradiated with the excimer laser 103 is once melted, re-solidified and crystallized, and becomes a polycrystalline (poly) silicon film 104. Step 3: Scanning the entire surface with the excimer laser 103,
As shown in FIG. 5 (c), the entire surface is a polycrystalline silicon film 104.
And Step 4: As shown in FIG. 5D, silane and nitrogen oxide N ₂
Gate oxide film 105 is formed on the surface of polycrystalline silicon film 104 by plasma CVD using an O mixed gas. Step 5: Next, a conductive film made of a metal or a doped silicon film is formed on the entire surface, and this is etched using a mask formed by photolithography to form a gate electrode 10.
6 is formed. Next, as shown in FIG. 5E, a source 107 and a drain 108 are formed by implanting impurities such as phosphorus, arsenic, and boron into the polycrystalline silicon film 104 by self-alignment using the gate electrode 106 as a mask. To form

[0005]

According to the above-described steps, the following problems occur.

[0006] On the other hand, when an amorphous silicon film is formed by plasma CVD and recrystallized by excimer laser annealing, in the initial stage of recrystallization in excimer laser annealing, as shown in FIG. 1
09 are formed randomly and countlessly. On this occasion,
The distance between the generated crystal nuclei 109 is at most about several hundreds of mm at the longest. As film formation or recrystallization proceeds, crystals grow with the crystal nuclei 109 as nuclei. The crystal growth proceeds isotropically with the crystal nucleus 109 as a center, and each becomes a crystal grain. However, the crystal nucleus 109
Because the space between them is narrow, the crystals collide with each other,
Lateral growth is suppressed, and crystal growth is mainly in the direction perpendicular to the glass substrate. Therefore, the grain size r of the polycrystalline silicon film 104 is at most about several hundreds of degrees.

[0007] Between the grains, discontinuous planes of crystals, so-called grain boundaries 110 are formed. The grain boundary 110 serves as a potential barrier, for example, when a current is to flow. If the particle size is small, one device contains many grain boundaries 110, so that the barrier potential increases, the silicon / silicon oxide interface characteristics and the silicon film quality characteristics decrease, and the electron mobility in the film decreases. For example, in a transistor formed using such a film, device characteristics such as an increase in leakage current and a decrease in on-current are caused.

Accordingly, an object of the present invention is to provide a manufacturing process for forming a polycrystalline silicon film having a large silicon crystal grain size and high electron mobility on an insulating substrate.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and comprises a step of forming a first film on which a crystalline silicon and an amorphous silicon are mixed on a substrate, and further comprising the steps of: Forming a second film made of amorphous silicon, and crystallizing the first and second films to form a polycrystalline silicon film.

The step of crystallizing the first and second films to form a polycrystalline silicon film includes a step of irradiating the second film with an excimer laser.

The step of forming the first film includes a step of exciting silane plasma near the substrate and irradiating the plasma with ions.

After the step of forming the first film, the irradiation of ions is stopped to shift to a step of continuously forming the second film, and the substrate is exposed to the air between the two steps. Not exposed.

The volume ratio between crystalline silicon and amorphous silicon of the first film is between 3: 1 and 1: 3.

The grain size of crystalline silicon contained in the first film is 2000 ° or less.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing a manufacturing process of a first embodiment of the present invention in order. Step 1: As shown in FIG. 1A, a microcrystalline film 2 containing microcrystals is formed on a transparent insulating substrate 1 made of glass or the like at about 100 °, and silane (SiH ₄ ) or disilane ( An amorphous silicon film 3 is formed to a thickness of about 400 ° by plasma CVD using a gas obtained by diluting higher order silane such as Si ₂ H ₆ ) with hydrogen. The microcrystalline film 2 is a film in which silicon crystals are scattered and mixed in amorphous silicon, and its manufacturing method will be described later in detail. The ratio of crystalline silicon to amorphous silicon contained in the microcrystalline film 2 is preferably about 1: 1. It is desirable that the ratio of the thickness of the microcrystalline film 2 to the thickness of the amorphous silicon film 3 is smaller in the microcrystalline film 2 than about 1: 1. Step 2: As shown in FIG. 1 (b), the microcrystalline film 2 and the amorphous silicon film 3 are irradiated with an excimer laser such as ArF, KrF, XeCl, etc., and are scanned and annealed. The amorphous silicon film in the region irradiated with the excimer laser is once melted, re-solidified and crystallized to form a polycrystalline (poly) silicon film 4. Step 3: A silicon oxide film having a thickness of 100 ° is formed on the entire surface by plasma CVD or thermal oxidation using a mixed gas of silane and nitrogen oxide N ₂ O to form a gate oxide film 5. Next, a conductive film made of a metal or a doped silicon film is formed on the entire surface at about 1300 °, and is etched using a mask formed by photolithography to form a gate electrode 6. Next, as shown in FIG. 1C, a source 7 and a drain 8 are formed by implanting impurities such as phosphorus, arsenic, and boron into the polycrystalline silicon film 4 by self-alignment using the gate electrode 6 as a mask. To form

Next, a method for forming the microcrystalline film 2 employed in this embodiment will be described. So-called plasma CV
D is a method of exciting silane plasma near the substrate and depositing it. In this method, when the temperature is low, amorphous silicon is deposited. On the other hand, in step 1, as shown in FIG. 2, silane plasma is excited near the insulating substrate 1, hydrogen ions generated by the ion source 11 are accelerated by the acceleration electrode 12, and hydrogen ions are Irradiate. Then, the amorphous silicon is locally melted by the energy of the hydrogen ions, and is solidified, whereby microcrystals as local crystal grains are randomly generated in the amorphous silicon. The volume ratio between crystalline silicon and amorphous silicon can be controlled by the amount of hydrogen ions to be irradiated and the energy to be irradiated. The crystal grain size contained in the microcrystalline film 2 formed by this method can be controlled by the amount of hydrogen ions, acceleration energy, substrate temperature, etc., and is set to be on the order of 1000 °.

The ions to be implanted are not limited to hydrogen, but may be, for example, ions of an inert gas such as argon, ions of a silicon compound, or electrons. If it is a hydrogen ion, it is easily bonded to a hydrogen atom of silane when irradiated with silane plasma, and the film formation rate is high. In addition, inert gas ions or electrons do not cause a chemical reaction with silicon deposited after film formation. In the case of silicon compound ions, the irradiated ions also contribute to the film formation, so that the film formation speed is high.

The microcrystalline film 2 can be formed by a method other than the above-described ion irradiation method, for example, by irradiation with a silicon ion beam or sputtering of silicon. The particular advantages of employing the ion irradiation method will be described below. In the above-described ion irradiation method, if the irradiation of ions is stopped, ordinary plasma CVD is performed. Therefore, if the ion irradiation is stopped after the microcrystalline film 2 is formed to a desired thickness, the process directly shifts to plasma CVD, and the amorphous silicon film 3 can be formed continuously. Since continuous film formation is possible, the film is not exposed to the air between the formation of the microcrystalline film 2 and the formation of the amorphous silicon film 3. Therefore, formation of a natural oxide film between the microcrystalline film 2 and the amorphous silicon film 3 can be prevented, and dust, carbon,
Intrusion of impurities such as oxygen and nitrogen can be prevented. Thus, a polycrystalline silicon film having higher electron mobility can be obtained. Further, the thickness of the microcrystalline film 2 can be freely set only by adjusting the timing of stopping the ion irradiation.

Next, the formation of the polycrystalline silicon film 4 will be described with reference to FIG. FIG. 3A is a cross-sectional view showing a state where a microcrystalline film 2 and an amorphous silicon film 3 are formed on an insulating substrate 1. The microcrystalline film 2 has a mixture of a crystalline portion 2a of crystalline silicon and an amorphous portion 2b of amorphous silicon. As described above, the grain size of crystalline silicon is 1000 °, and the volume ratio between crystalline silicon and amorphous silicon is about 1: 1. Therefore,
The diameter of the amorphous portion 2b is also approximately 1000 °. FIG. 3B is a cross-sectional view showing a state after excimer laser annealing has been performed and the polycrystalline silicon film 4 has been changed. The amorphous portion 2b melted by the excimer laser is integrated with the crystal portion 2a of the microcrystalline film 2 as a nucleus, and the crystal nucleus 2a grows as indicated by an arrow. As a result, the particle size was 2000 mm.
Of polycrystalline silicon 4a is formed. Also, polycrystalline silicon 4b having a grain size of 4000 ° may be formed by crystal growth using a plurality of crystal parts 2a as nuclei or by combining a plurality of crystals into one during the crystal growth process. Thus, the polycrystalline silicon film 4 formed in the present embodiment has a grain size of 2000 to 4000 °.

Here, the volume ratio between crystalline silicon and amorphous silicon will be described. First, when there is more crystalline silicon than amorphous silicon, the interval between the crystal parts 2a becomes narrow. For example, if the volume ratio between crystalline silicon and amorphous silicon is 3: 1, the crystal part 2
If the particle size of a is 1000 °, the crystal part 2a
The distance between them is approximately 300 °. When excimer laser annealing is performed in this state, the grain size of polycrystalline silicon grown by using one crystalline silicon as a nucleus has a grain size of 1300 °.
However, the polycrystalline silicon film 4 having good film quality is not obtained. Conversely, if there is more amorphous silicon than crystalline silicon, the spacing between the crystalline portions 2a will be wider. For example, when the volume ratio between crystalline silicon and amorphous silicon is 1: 3, the grain size of the crystalline portion 2a is 1000Å.
, The distance between the crystal parts 2a is about 3
000Å. When excimer laser annealing is performed in this state, a different crystal having no crystal part 2a as a nucleus is generated and grown between the crystal parts 2a. As a result, the grain size of the polycrystalline silicon is also about 2000 °, and the polycrystalline silicon film 4 having good film quality is not obtained. Therefore, crystalline silicon and amorphous silicon are almost equal in volume ratio of 1: 1.
Is desirable. However, if the grain size of the crystal part 2a is too large, the interval will be wide even if the volume ratio is 1: 1. Therefore, it is desirable that the grain size of crystal portion 2a be 2000 ° or less.

By the way, annealing with an excimer laser requires fine adjustment of laser energy. This is because if the laser energy is too low, the amorphous silicon will not melt sufficiently, and if the laser energy is too high, the temperature will be too high, and the crystal growth rate will increase, resulting in a smaller crystal grain size of the polycrystalline silicon. This is because FIG. 4 shows a change in the crystal grain size of polycrystalline silicon with respect to the energy of the excimer laser. For example, 200
It is assumed that a polycrystalline silicon film having a crystal grain size of 0 ° or more has the required quality. First, a curve shown by a solid line is a curve 500 as an example of a conventional forming method.
The crystal grain size of the polycrystalline silicon film obtained by irradiating the amorphous silicon film with an excimer laser is shown in FIG.
When the energy of the excimer laser is increased, the crystal grain size of the polycrystalline silicon formed accordingly increases. When the value exceeds a certain value, the crystal grain size of the polycrystalline silicon becomes smaller as the energy of the excimer laser increases. Therefore, the energy width of the excimer laser that can obtain a non-defective polycrystalline silicon film is the region indicated by a in the figure. On the other hand, according to the present embodiment indicated by the dashed line, the crystal grain size of the polycrystalline silicon film exceeds 2,000 ° with a lower energy excimer laser, and the energy region where the grain size becomes larger than the conventional one is obtained. Through the above, the particle size is 2,000 mm or more up to the energy higher than the conventional one. Therefore, the usable energy region of the excimer laser according to the manufacturing method of the present embodiment is the region indicated by A in the figure, and it is possible to obtain a non-defective product with a wider energy width than the conventional one. Since the energy of the excimer laser requires fine adjustment, a wide usable energy range of the laser leads to an improvement in the production yield.

Further, both the conventional example and the present embodiment have been described so that the thickness of the polycrystalline silicon film 4 is 500 °. This is because, when excimer laser annealing is performed, if the film thickness is small, the heat capacity is small, resulting in excessive heating, and the polycrystalline silicon grain size becomes small. In other words, the energy region of the excimer laser that can be used for annealing is reduced. This is for avoiding becoming narrow. On the other hand, according to the manufacturing method of the present embodiment, even if the thickness of the polycrystalline silicon film 4 is set to, for example, about 300 °, the energy region of the excimer laser which is almost the same as that of the related art can be used. That is, the film thickness can be further reduced. If the film thickness can be reduced, it can be made flatter after forming circuits and various electrodes.

Incidentally, an amorphous silicon film 3 may be formed on the substrate 1 and the microcrystalline film 2 may be formed thereon.
Further, an amorphous silicon film 3 may be formed thereon. In short, if the microcrystalline film 2 and the amorphous silicon film 3 are formed adjacent to each other and excimer laser annealing is performed together,
Crystals grow on the amorphous silicon film 3 using the crystals in the microcrystalline film 2 as nuclei.

In the present invention, glass has been described as an example of the insulating substrate 1. However, other insulating substrates, for example, ceramic or acrylic, may be used as the substrate.

In this embodiment, the transistor is formed by using the polycrystalline silicon film 4. However, the present invention is not limited to this. For example, if the wiring is used, a low-resistance wiring can be realized. A large polycrystalline silicon film is useful for forming any semiconductor element.

[0026]

As described above, according to the present invention, a first film in which crystalline silicon and amorphous silicon are mixed on a substrate and a second film made of amorphous silicon are crystallized to form polycrystalline silicon. Since the film is formed, a polycrystalline silicon film having a large grain size and high electron mobility can be obtained.

When the first and second films are crystallized by irradiating an excimer laser, the usable energy width of the excimer laser is wide, so that the production yield can be improved.

Further, since the step of forming the first film includes the step of exciting silane plasma near the substrate and irradiating the plasma with ions, the volume ratio of crystalline silicon to amorphous silicon can be easily controlled. can do. Furthermore, the first
After the step of forming the film, the irradiation of ions can be stopped to shift to the step of continuously forming the second film, so that the substrate is not exposed to the air between the two steps,
A high-quality polycrystalline silicon film can be obtained, and the thicknesses of the first and second films can be easily controlled.

Since the volume ratio of crystalline silicon to amorphous silicon of the first film is between 3: 1 and 1: 3, a polycrystalline silicon film having a large grain size can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method for manufacturing a polycrystalline silicon film of the present invention.

FIG. 2 is a cross-sectional view illustrating a method for manufacturing a microcrystalline film according to the present invention.

FIG. 3 is a sectional view showing the manufacturing method of the present invention in detail.

FIG. 4 is a diagram showing a change in the grain size of polycrystalline silicon depending on the energy of excimer laser annealing.

FIG. 5 is a cross-sectional view showing a conventional method for manufacturing a polycrystalline silicon film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Microcrystalline film 3 Amorphous silicon film 4 Polycrystalline silicon film 5 Gate insulating film 6 Gate electrode 7 Source region 8 Drain region

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/336 H01L 29/78 627G F term (Reference) 2H092 GA59 JA25 KA04 MA08 MA27 MA30 NA24 NA29 PA01 4K030 AA06 AA17 BA29 BB04 BB05 BB13 CA06 DA09 FA01 LA18 5F052 AA02 BB07 CA04 DA01 DA02 DB03 FA01 FA19 JA01 JA10 5F110 AA01 AA06 BB01 CC02 DD01 DD02 EE02 EE09 FF02 FF23 FF30 GG02 GG13 GG16 GG25 PP40 HJPP

Claims (6)

[Claims] A step of forming a first film in which crystalline silicon and amorphous silicon are mixed on a substrate; and a step of forming a second film made of amorphous silicon on the first film. Crystallizing the first and second films to form a polycrystalline silicon film. 2. The method according to claim 1, wherein the step of crystallizing the first and second films to form a polycrystalline silicon film includes a step of irradiating an excimer laser on the second film. A method for forming a polycrystalline silicon film according to the above. 3. The step of forming a first film on which crystalline silicon and amorphous silicon are mixed on the substrate includes exciting silane plasma near the substrate and irradiating the plasma with ions. The method for forming a polycrystalline silicon film according to claim 1, wherein: 4. After the step of forming the first film, the irradiation of the ions is stopped to shift to a step of continuously forming the second film, and between the two steps, The method according to claim 3, wherein the substrate is not exposed to the atmosphere. 5. The formation of a polycrystalline silicon film according to claim 1, wherein the volume ratio of crystalline silicon to amorphous silicon of the first film is between 3: 1 and 1: 3. Method. 6. The method according to claim 5, wherein the grain size of the crystalline silicon contained in the first film is 2000 ° or less.
3. The method for forming a polycrystalline silicon film according to item 1.